The present invention relates to a white balancing apparatus in use for a video camera.
In general, although white is sensed as it is by the human visual system under any light source, e.g., sun light, fluorescent light or incandescent light, it becomes red or blue depending on the light source, through image pickup device of a video camera. This is because of a color temperature. The higher color temperature makes white blue and the lower color temperature makes white red, thereby disabling to realize a proper color.
The light source is varied in its energy distribution according to wavelength, depending on its type, as shown in FIG. 1. That is to say, the sun light has a constant energy distribution according to wavelength, as shown in FIG. 1A, the incandescent light whose color temperature is low has the distribution of energy which increases in proportion with wavelength, as shown in FIG. 1B, and the fluorescent light whose color temperature is high has the distribution of energy which decreases in disproportion with wavelength, as shown in FIG. 1C.
Human visual system has a color adaptive capability with respect to such light source by memory. However, chargecoupled device (CCD) imager does not have the color adaptive capability. Thus, the information on the light source is estimated from the signal input from the CCD imager to minimize the affect of the light source.
As described above, the white balance implements an object color varied according to light source whose energy distribution is different depending on wavelength as that under the sun light and will be explained with reference to FIGS. 2A and 2B.
FIGS. 2A and 2B explain the process of treating the white balance by the white implementation under the incandescent light.
If the energy of the light source depending on the wavelength of the incandescent lamp is increasingly distributed proportionately to the wavelength as shown in FIGS. 2A-1 and the reflection index of the object having white color components is as shown in FIG. 2A-2, the white through the incandescent lamp is recognized practically as good as a red. In order to process the white balance, gain is multiplied with the light source whose energy distribution depends on wavelength so that the object can be recognized as a white as through the sun light.
That is to say, if the energy of the light source depending on the wavelength of the incandescent lamp as shown in FIG. 2A-1 is multiplied with the energy depending on the wavelength of the white object as shown in FIG. 2A-2, the energy of the color as recognized under the incandescent lamp, with which the gain corresponding to the light source having the magnitude opposite to the energy of the light source depending on the wavelength of the incandescent lamp is multiplied to be recognized as the original white object under the sun light.
As shown in FIG. 3, the conventional white balancing apparatus includes a signal processor 11 for a video camera, a blanking portion 12 to which red component signal R, green component signal G and blue component signal B output from the signal processor 11 are input for performing the white balance, a blanking detector 15 for outputting the blank pulse generated according to the magnitude of the green component signal G output from the signal processor 11 to the blanking portion 12, an integrator 13 for respectively integrating the non-blanked red component signal R, green component signal G and blue component signal B, a switch for inputting and switching the integrated signal for each field, i.e., 1/60 seconds interval, a comparator 17 for receiving the signal output from the switch 14 as an inverted input, a comparison signal outputting portion 16 for generating a jagged wave by receiving a reference signal Ref output from the signal processor 11 and then outputting as the non-inverted input of the comparator 17, and a white balance controller 18 for inputting the pulsewidth modulation signal output from the comparator 17 and then outputting red and blue color control signals to the signal processor 11.
The operation of the conventional white balancing apparatus having the aforementioned configuration will now be described.
The red component signal R, green component signal G and blue component signal B are output from the signal processor 11. Among them, the level of the green component signal G is determined in the blanking detector 15. If the level thereof exceeds a constant value, the green component signal G is recognized as the light source or high luminance portion to then generate blanking pulse. The blanking pulse output from the blanking detector 15 is input to the blanking portion 12 to then blank the three color component signals, i.e., the red component signal R, green component signal G and blue component signal B are output from the signal processor 11.
Also, as the result of the determination of the blanking detector 15, if the green component signal G output form the signal processor 11 is below a constant value, it is recognized as a general object so that the blanking pulse is not generated. At this time, the non-blanked three color component signals, i.e., the red component signal R, green component signal G and blue component signal B, are integrated in the integrator 13, respectively, and thereafter, are switched in the switch 14 in each field to then be supplied to the non-inverted input port of the comparator 17.
Meanwhile, the reference signal Ref of the three color component signal is turned into a jagged wave in the comparison signal outputting portion 16 to then be supplied to the non-inverted input port of the comparator 17. The comparator 17 compares the signal output from the switch 14 and the jagged wave output from the comparison signal outputting portion 16 to then output to the white balance controller 18 the pulsewidth modulation signal whose pulsewidth is varied depending on the signal level output from the switch 14.
The white balance controller 18 detects each width of the input pulsewidth modulation signal, calculates red component signal pulsewidth/green component signal pulsewidth (R/G) and blue component signal pulsewidth/green component signal pulsewidth (B/G) and outputs red and blue control signals which allows the calculated results to be `1` that is R/G=B/G=1, to the signal processor 11. This is because it is assumed that R=G=B in the case of achromatic color signals, white, gray and black color signals.
Green component signal G used in the blanking detector 15 of the aforementioned conventional white balancing apparatus excludes the signal components of the light source or high luminance during performing the white balance but makes only the signals of an ordinary luminance to be used as the signals for performing the white balance.
However, since the conventional white balancing apparatus performs the white balance by receiving the chromatic color signal of the photographed object itself together with color signal caused by illumination, if the photographed object itself has the chromatic color component such as red or blue component, irrespective of the light source, the color signal is also used as information for performing the white balance to decolorize the color signal.